Comments on OTTC from the HWT blog: (http://goesrhwt.blogspot.com/2011/06/ewp-end-of-week-debrief-10-june.html)
Overshooting-top / Thermal
- (Thursday event - KS/OK) None were detected when forecasters expected to see detections, so was not used, especially with the rapid updates of radar data.
- Need to remember to turn icon density to "MAX" within AWIPS or some detections will be lost.
- Looked at pretty much every day... for the most part, operator identified OTs occurred before the algorithm did.
Comments on OTTC from the HWT blog: (http://goesrhwt.blogspot.com/2011/06/daily-debrief-9-june.html)
Overshooting-tops / Thermal
- Thermal couplet showed up over SW WI, but warning was already issued and radar was showing clear signals of severe weather.
- Interesting to see all the thermal couplets over northern Maine... might be a good case to examine.
- There were many overshooting tops over the WI area, however forecasters were too engulfed in the rapidly updating radar data.
Comments on OTTC from HWT blog: (http://goesrhwt.blogspot.com/2011/05/end-of-week-debrief-27-may.html)
Overshooting-top / Thermal
- (26 May event) One couplet was over some leading cells along the PN/MD line... the clouds behind that were masked by cirrus and may have limited the detection. When it did trigger, it well differentiated that cell from the rest of the scene.
More comments from HWT Blog: (http://goesrhwt.blogspot.com/2011/05/ewp-forecaster-debrief-26-may.html)
Overshooting-tops / Thermal
- Not many were seen, but those that were tended to be near the center of the upper low.
- Those that were seen did coincide with instances of increases in reflectivity aloft.
- Usefulness within warning ops very minimal because of lack of detections.
(Reply by Kris Bedka:
Given that the Overshooting Top /
Thermal Couplet developers are not there with the forecasters, we may
not have a good handle on what you are seeing. But from the daily
OT/TC plots (see below), it would see that OT detections have been
quite frequent near severe weather reports. One must stress that
enhanced-V (i.e. TC) storms are infrequent and our ability to
objectively detect them is limited by current GOES spatial
More from HWT: (http://goesrhwt.blogspot.com/2011/05/overshooting-tops-are-being-detected.html)
The UWOTTC algorithm is consistently identifying overshooting tops over the state of Indiana. The above sequence of images (valid from 1902 UTC to 1945 UTC) shows numerous overshooting tops and their associated visible imagery counterparts. No thermal couplets have been detected with any severe storms as of yet, but this is not a surprise with how hard it is to detect the couplet features with the course resolution of GOES imagery.
Overshooting-top / Thermal
- Later on in the evening we saw some detections, but earlier on we could see some enhanced-v and OT signatures in the imagery, but none were detected.
- If you had someone in operations during warning times that was just doing mesoanalysis and telling forecasters that a detection occurred would be very useful... I get too involved with interrogating radar data during warnings.
- Rapid-scan, high resolution satellite data would definitely make this more useful.
- Would like to see an overshooting top collapse product... maybe an alert.
- Only had a chance to look at the icon detections.
Detections or magnitudes more useful?
"I looked at the detections only."
Did you see any correlations between OT detections and features developing on radar?
"Reflectivity was increasing above certain (height) levels at that time."
How often did the product correctly detect OTs that you could see on VIS/IR?
"For a warning operator, I don't see this product adding much value to an on-going event..." (from survey) Why is that? Lack of detection, timeliness, applicability of product?
"Radar was more important... mix between timeliness and applicability."
"Get a good a western example case where you don't have radar."
"Maybe knock out some radars in a WES case."
Forecasters mentioned they don't know what overshooting tops tell you... need more examples of this in training/literature.
Losing confidence by high threshold when you can see in visible... maybe a training issue... when you see a detection maybe it's more serious than a typical OT.
Combining with storm top divergence... "I think there's a lot of potential there."
Forecasters requested thermal couplet/overshoot detections in one product... hard to watch two different products... takes up a window in their D2D... "The more we can combine the better."
More : (http://goesrhwt.blogspot.com/2010/05/ewp-week-2-debrief.html)
- All week continued to lag radar signals of severe.
- No thermal couplets saw in real time all week
- Forecasters understand it should work better with 2 km data.
- Similar comment a UWCI about accumulated product
- Overall was not very useful in warning operations.
"I could make out that it was an OT before it could... about 30 minutes before. I guess this was because of the coarse grid, but by the time an OT was detected I already had a hook echo with a tornado on the ground."
We showed the 24-hour detections of overshoots and thermal couplets. The thermal couplets were much more confined to severe areas and the overshoots were much more widespread and matched with areas of CG activity, but both seemed to lag occurrence of severe weather.
- When not looking at discrete supercells, it may be more useful in detecting embedded supercells
- Need to establish (and communicate) better the relationship between OT and severe weather potential
- Erosion of OT would be much more useful than a detection... updraft collapse or weakening... OT magnitude trends would be much more useful
- Difference the cloud-top temp of the overshoot with model temp of level to give an idea of height above EL for instance would be interesting
- Detection not important alone, especially when seeing core aloft on radar... However, where radar coverage sparse, might be more useful (eg. out west)
General discussion on overshooting-tops...
"Overshooting-tops are much more common than I was led to believe in school."
"We did observe that the reflectivity core aloft did intensify when an overshoot was detected."
"Would be interesting to see how they correlate with the occurrence of BWERs. If we had temporal continuity (a continuous) detection, we would expect to see a BWER."
"Overshooting dissipation would be interesting in determining the occurrence of tornado or large hail at the surface."
"If we had rapidly updating satellite, it would be much more useful."
"Might also be useful to have a OT track product... would help in determining storm (updraft) motion."
From the 2009 Spring Experiment Final Report:
In general, while forecasters found the idea of the OTTC product exciting, the limitations of the current observational system severely limited the OTTC product as demonstrated in severe weather warning operations. There were instances of “many overshooting tops were observed on visible satellite that were not detected by the OTTC product” mentioned within the online surveys and during EWP daily briefings. Since the OTTC product relies on spatial tests to detect IR features associated with overshooting-tops and thermal couplets, the coarse IR resolution of GOES-13 was often unable to detect these features since they are generally smaller than the GOES-13 IR footprint. The product has been shown to work well on current low-earth orbiting satellite instruments, such as MODIS on NASA’s Terra and Aqua satellites (see Bedka et al. 2009), whose spatial resolution is better suited to detect these features. The forecasters would like to see the product demonstrated using these high spatial resolution datasets in an operational sense, but unfortunately that is not currently possible as MODIS data is only available twice a day. . . . .
Forecasters mentioned that OTTC detections would provide a useful tool in identifying the most intense storms within a scene without having to interrogate radar or base satellite data, as shown in this response from the online survey:
“The OTTC product was most useful in indicating locations where storm strength was at a relative maximum… Quickly highlighting the strongest thunderstorms on the visible satellite imagery where it can be hard to distinguish storms due to similar brightness.”
Forecasters also mentioned that the product “may be useful to verify strong updrafts in MCS's” that may be hard to detect using radar or other satellite techniques, as shown in this online survey response:
“Not really a helpful tool for isolated supercells, because the overshooting top is fairly obvious in visible/IR imagery and easy to diagnose. For this reason, I think it would be more useful in MCS's when the overshooting tops are less obvious.”